change the article description to TextField type

A text field makes it easier to edit the description than with a
CharField because the text box is bigger.

django/didgeridoo/webshop/models.py

@@ -46,8 +46,8 @@ class Category(models.Model):
 
 class Article(models.Model):
     name = models.CharField(max_length=200)
-    description = models.CharField(max_length=2000)
     category = models.ForeignKey(Category, null=True)
+    description = models.TextField(max_length=2000)
     stock = models.FloatField(max_length=5)
     status = models.ForeignKey(ArticleStatus)
     price_in_chf = models.DecimalField(max_digits=19, decimal_places=2)